NERVOUS SYSTEM OF ORGANIC LIFE.
GENERAL REMARKS.
No anatomist has yet considered the nervous system of the ganglions in the point of view in which I shall present it. This point of view consists in describing each ganglion as a distinct centre, independent of the others in its action, furnishing or receiving particular nerves as the brain furnishes or receives its own, having nothing in common, except by anastomoses, with the other analogous organs; so that there is this remarkable difference between the nervous system of animal life, and that of organic life, viz. that the first has a single centre, and that it is to the brain that every kind of sensation comes, and that it is from it every kind of motion goes; whilst in the second, there are as many little separate centres, and consequently little secondary nervous systems, as there are ganglions.
We know that all anatomists, even those who, without affixing to the expression any very definite meaning, have called the ganglions little brains, have taken them for dependancies, for enlargements of the nerves, in whose course they are found; and as most of them are met with in the great sympathetic, they have presented them as a distinctive character of this nerve. But from the general idea I have just given of the ganglions, it is evident that this nerve has no real existence, and that the continuous thread that is observed from the neck to the pelvis, is nothing but a succession of nervous communications, a series of branches that the ganglions placed above each other, send reciprocally to each other, and not a nerve going from the brain or the spine.
The first considerations that induced me to think that the great sympathetic is not a nerve like the others, but a series of anastomoses, were the following. 1st. These communications are often interrupted, without any inconvenience, in the organs to which the great sympathetic goes. There are subjects, for example, in whom is found a very distinct interval between the pectoral and lumbar portions of this pretended nerve, which seems cut in this place, because the last pectoral ganglion and the first lumbar do not send branches to each other. I have often seen also the sympathetic nerve cease, and afterwards appear again between two ganglions and from the same cause, whether in the loins, or in the sacral region. 2d. Every one knows that the opthalmic ganglion, the spheno-palatine, &c. are constantly distinct, and that they do not communicate by their branches except with the cerebral nerves. It uniformly happens that there is between them and those of the great sympathetic, what we sometimes see between these last, viz. a complete deficiency of communication. 3d. In birds, as has been observed by Cuvier, the superior cervical ganglion is also found constantly distinct; it never communicates with the inferior. The filament which in quadrupeds descends the length of the neck, is wanting in them. In many other animals we frequently find interruptions in this succession of anastomoses of ganglions, which constitute what is called the great sympathetic. 4th. The communications of the ganglions are usually made by a single branch; but sometimes many go from one of these organs to the other, so that if the great sympathetic was a nerve like the others, it would present, in this respect, an arrangement wholly different from that of the cerebral nervous system. 5th. Whence does the great sympathetic arise? From the sixth pair? But all the nerves diminish as they go from the brain towards the organs; but this presents then an arrangement entirely different; it increases as it sends off branches. Does it arise from the spinal marrow? But then the branches with which it furnishes a region would come from the branches that it receives from the spinal marrow in this region. Thus the great and small splanchnic would arise from certain intercostal pairs, now they are evidently much larger, the first especially, than the sum of the branches from which they would derive their origin. Observe then that all anatomists have been of a different opinion upon the origin of the great sympathetic. How could they agree upon a thing that has no real existence?
These different considerations render probable the opinion that I have entertained for some time, that the great sympathetic nerve does not really exist, that this cord is but a succession of communications between little nervous systems placed above each other, and that it is not essential that these communications should exist, as is seen constantly between the ophthalmic ganglion and the spheno-palatine, between that and the superior cervical, of which many animals furnish examples. Then I began to regard each ganglion as a separate centre of a little nervous system, wholly different from the cerebral, and distinct even from the little nervous systems of the other ganglions. By considering the functions of the nerves going from these centres, I became more and more convinced that they did not belong to the cerebral system. In fact, these nerves have properties very different from theirs, as we shall see; they do not serve for sensations; they have uniformly no connexion with voluntary locomotion; we see them only in the organs of internal life; hence why they are found concentrated in the trunk, in the thorax and abdomen particularly; why they are not met with in the head, where almost all the organs belong to animal life; why they are not seen in the extremities, which are exclusively dependant upon this life.
Distributed almost every where to the organs of the internal life, the ganglions and their nerves derive their character from it; and this is it. 1st. They are not symmetrical; thus the nerves of all the plexuses of the abdomen, those of the cardiacs, &c. have a remarkable irregularity. 2d. There are numberless varieties in the form of these plexuses and in that of the ganglions; it is thus that, sometimes lenticular, sometimes triangular, sometimes divided into many portions, that which is under the diaphragm is never seen twice alike. Hence the error of every name derived from the figure; a remark that is applicable generally to the organs of internal life. We might rather borrow the names of forms for animal life in which these forms are more invariable. On the other hand, the existence of many ganglions varies; sometimes there are three of them in the neck, at others but two. The arrangement of one side does not produce a similar one on the other. I have frequently remarked that the number of filaments arising from the superior cervical ganglion differs very much from those that take their origin from the opposite side. There are two analogous organs at each side; but several attributes of structure destroy the general character of symmetry; it is like the lungs and the kidnies. We can, then, establish as a distinctive character between the two nervous systems, the symmetry of one and the irregularity of the other; now, this character is one of those which distinguish the two lives, as I have remarked before.
From all this it is evident that a line of demarcation separates the nerves of the ganglions and those of the brain, and that the method is inaccurate which considers them as forming a single nerve, arising by some origin from this last. Their communications no more prove it to be a general nerve, than the branches which pass from each of the cervical, lumbar, or sacral pairs, to the two pairs that are superior or inferior to it. Notwithstanding these communications, we consider each pair in a separate manner, and not as one nerve by their union. So that each ganglion should be described separately, notwithstanding the branches it sends to others.
The description of the system of the ganglions should be analogous to that of the cerebral nerves. For example, I describe first the lenticular ganglion, as was done for the brain; then I examine its branches, among which is found the great splanchnic; for it is very improper to say that this nerve gives origin to this ganglion. The same in the neck, in the head, &c. each ganglion is first described; then I treat of its branches, among which are found those of communication. There are, then, almost as many descriptions as there are separate ganglions. For example, we ought not to treat of the ophthalmic nerve with the common motor; to be convinced of this, it is sufficient to see how much the ciliary nerves differ from the others, which, belonging to animal life, are also contained in the orbit.
From all that has been said, it is evident that there are two things to be examined in the nervous system of organic life, 1st. the ganglions; 2d. the nerves that go from them.
ARTICLE FIRST.
OF THE GANGLIONS.
I. Situation, forms, relations, &c.
The ganglions are little reddish or greyish bodies, situated in different parts of the body, and forming so many centres, from which goes an infinite number of nervous ramifications. Their position most generally is along the vertebral column, where are seen successively below each other, the superior and inferior cervical, the intercostal, the lumbar, and the sacral. It is these especially whose communicating branches form the great sympathetic. But besides these ganglions, which are placed as it were in a row, we find many separate ones in different parts, as the ophthalmics, the sphenopalatines, the maxillaries in the head, as also the semilunars in the abdomen. In the thorax there are none thus separate; though sometimes we see a small one at the base of the heart.
Besides the ganglions uniformly seen, there are often accidental ones, if we may so say; such are those that are sometimes found in the hypogastric plexus, in the solar even, at some distance from the semilunar, in the middle part of the neck, &c. On the other hand, some of those that are usually met with are oftentimes not found, as some of the lumbar, sacral, maxillary, &c.; so that it appears that there is really an essential difference between the ganglions under the relation of existence. The superior cervical, the semilunar, the ophthalmic, &c. are always found; they appear to be essentially necessary to the action of the organs to which they furnish nerves. Most of the others may be wanting on the contrary, and be supplied by those of the neighbouring ones, or by others formed not in the ordinary anatomical order.
All the ganglions are generally in a deep situation. Destitute of a bony covering analogous to that of the brain, they are not less powerfully protected against the action of external bodies. It is this deep position, that prevents us from making experiments upon almost all of them, from making those at least which require that the animal should live a certain time after they have been made. It is this which will undoubtedly keep up for a length of time the obscurity that hangs over the functions of these organs.
The form of the ganglions is extremely irregular. In general they are round; but sometimes they are long, as the superior cervical; sometimes the ganglion is a species of triangular body, with obtuse and round ends, as the ophthalmic; sometimes the form is semilunar, like that which has this name, &c. Generally these forms are very variable, as I have said; the most uniform is that of the superior cervical.
Embedded in a quantity of cellular texture, all the ganglions are separated by it from the neighbouring organs. Almost all of them are so disposed, that they experience but little motion from these organs, and cannot receive it from any of the vessels that enter them. Those situated along the vertebral column especially, present this phenomenon, very different from that which takes place at the brain, whose functions are essentially connected with the constant agitation that the blood imparts to it, and very different from that which we observe in the plexuses of nerves coming from these same ganglions.
II. Organization.
The ganglions have generally in the adult a reddish colour very different from that of the nerves; sometimes they are greyish. When opened, they present a soft, spongy texture, resembling considerably at first view that of the pretended lymphatic glands.
This texture has nothing in common with the cerebral substance, nor with that which occupies the canal of the nervous coat. These two last should rather be ranked in the class of fluids, as I have said; their substance is a pulp, a real jelly. Thus they have not any of the properties of solids. They do not harden like horn; the kind of hardening, the result of the contact of alkohol, of the acids, and of caloric, is wholly different from the horny hardening. It is analogous to the hardening of the white of an egg. On the contrary, the texture of the ganglions hardens like horn in an evident manner, a phenomenon which is characteristic of all the solids, except the epidermis, the nails, and the hair, which make a separate class. Treated by the acids, the ganglions, after wrinkling, hardening like horn and hardening gradually, soften and become fluid.
Boiling produces a phenomenon nearly analogous; 1st. horny hardening and hardening at the instant the water boils; 2d. continuance of this state for half an hour; 3d. softening gradually brought on; when this last is complete, the effect of the boiling is finished. In this state, the ganglions are all different from the nerves submitted to the same experiment. I have observed also in veal, that they have a very different taste from that of the nerves, a method of research which should not be neglected in attempting to ascertain the difference of the nature of the organs. In fact, as we do not yet know the difference of the principles which enter into the composition of each, we should be satisfied with the difference of the qualities.
The alkalies act a little upon the ganglions, which they tend to dissolve, and which they do partly dissolve, if they are very caustic. But this solution is infinitely less prompt and less easy than that of the cerebral pulp by the same re-agents. The ganglions resist putrefaction as much and even more than the nerves; this forms also a very remarkable difference between them and the cerebral substance. In general, we cannot establish any kind of analogy between them.
The texture of the ganglions appears in nowise fibrous; there is absolutely no linear, filamentous appearance, &c. upon simple inspection. Homogeneous, if we may so say, in its nature, it presents every where an uniform aspect when cut in slices. However the celebrated Scarpa has considered the ganglions as resulting from a kind of expansion of the nerves, into an infinite number of extremely delicate fibres, which interlace with each other, and which become very distinct by maceration. I have not repeated all his experiments, which appear to me extremely difficult. I refer then to his work, and to the plates it contains. I would observe only that there is certainly something else in the ganglions, besides a simple division of the nerve into extremely fine threads. In fact, mere inspection is sufficient to establish between them the greatest difference. There is as evident a demarcation between the ganglions and the nerves, as between those of the brain and the brain itself. 1st. Difference of colour, reddish or greyish tinge in some, white in others; 2d. difference of consistence, of external qualities, &c.; 3d. difference of properties. If the nerves coming from the spinal marrow make only an expansion, in their passage, in the ganglions, by delicate filaments, there would then be only a difference of form and not of nature; the properties would be the same. Why then are they so different as I shall prove hereafter? Why, as a nerve goes from a ganglion, does it not communicate more voluntary motions? 4th. Why has not nature placed ganglions in the nerves of the extremities as in those of the other parts? If there is only a division of the nerve into finer filaments, in the ganglion, why is there not a proportion between the filaments that enter on one side, and those that go out at the opposite? In fact, those that enter into the superior cervical above, if they only expanded their filaments in this ganglion, and united afterwards to form those that go off below, would be equal in respect to size to those that go from it; all the ganglions would exhibit this constant relation between the nerves of one side and those of the opposite; now, it is sufficient to examine them to be convinced that an inverse arrangement exists. 6th. The ganglions ought always to be in proportion to the size of the nerves which form them by spreading their fibres. Why then are the intercostal ganglions so small, and the trunks that unite them, or rather that give origin to them and which go from them afterwards as we see in the usual manner, so large? Why on the contrary, is the superior cervical ganglion so large, and its branches so small? 7th. How can be explained the frequent interruptions between the ganglions in man, which are constant in many animals, if there is a continuity between the nervous filaments that enter the ganglions above, and those that go from them below? 8th. How does it happen that the ganglions and their nerves do not follow an exact proportion as to development with the cerebral nerves, if these form them by expanding? 9th. Why has not pain the same character in each species of nerves?
I have no opinion as to the nature or the functions of the ganglions, because I have no fact to support me; but there is certainly something more in their texture, than a mere expansion of nervous filaments. Scarpa admits a peculiar matter which separates these filaments; but this substance ought to predominate considerably, as the ganglion surpasses in size the nerves which are thought to give origin to it. Now I have never seen this substance; I do not know what it is; all is solid when the ganglion is cut. I think then by admitting, even to a certain extent, the internal arrangement that this author has observed in the ganglions, we cannot describe these organs in the point of view in which he has presented them.
We know but little of the alterations that diseases produce in the texture of the ganglions. I have already many times examined in diseases of the heart, of the liver, of the stomach, the intestines, the ganglions that send nerves to these viscera; they have never appeared to me to have undergone any change. In cancers of the stomach in the very last stage, in which all the cellular texture is engorged, and in which all the lymphatic glands are considerably swelled, I have always found the semi-lunar ganglion untouched, except however in one case where it was enlarged and its density a little increased. At another time I found this same ganglion of the size of a small nut, with a cartilaginous substance in its centre, resembling the stone of it, in the body of a man brought to the Hôtel Dieu on account of periodical mania. Some authors have thought, and I suspect the same thing also, that the hysteric paroxysms, which begin by a contraction at the epigastric region, and in which the patient feels a ball mount up even to the throat, arise from some affections of the semi-lunar ganglions, from the solar plexus and the communications which go from ganglion to ganglion, even to the neck. However two bodies that I have opened lately, exhibited no alteration, though during life the subjects had been frequently attacked with these paroxysms; but they may arise evidently from the ganglions and the epigastric plexuses, without their being altered in their structure, as a number of cerebral affections leave after them no trace in the brain. This point deserves particular examination.
It does not appear that the texture of the ganglions is surrounded by a peculiar membrane. The cellular texture is only condensed in their neighbourhood; it then becomes very consistent, and much contracted around them. It there has the nature of the sub-mucous, the sub-arterial textures, &c.; it never contains fat. There is then truly around the ganglions, as around the arteries, under the mucous surfaces, &c. the two kinds of cellular texture of which we have spoken in treating of the organization of this texture, and which differ so essentially from each other in their nature, and even in their properties. It is the second kind, which is analogous to the sub-arterial texture, &c. which forms the peculiar membrane admitted by some authors.
By examining attentively the interior of the ganglions, we see that there is but very little cellular texture there. I have found this texture constantly destitute of fat; thus the alkalies do not form a saponaceous deposit upon them, as upon the cerebral nerves when plunged in their solution. I have examined many ganglions in this way, on account of the opinion of Scarpa, who believes that these organs are penetrated with this fluid, at least in fat people.
The ganglions receive many blood vessels. These penetrate them from all sides, run first in a kind of cellular covering that surrounds them, then entering their texture, ramify and are lost there in numerous anastomoses, and in continuation with the exhalants that carry nutritive matter. Fine injections show a great quantity of vessels in these little organs. Nutrition supposes exhalants and absorbents there.
III. Properties.
It is difficult to analyze the properties of texture in the ganglions. As to vital properties, they cannot grow, live and be nourished without organic sensibility, and without insensible contractility of the same kind. Animal and sensible organic contractility do not exist there evidently. As to animal sensibility I have observed the following circumstance. As in opening the abdomen of an animal, of a dog, for example, he lives very well for some time, and remains even calm after the first moments of suffering; I have waited for this calm that succeeds the agitation arising from the incision of the abdominal parietes, then laid the semi-lunar ganglion bare, and irritated it powerfully; the animal is not agitated, whilst when I excite a cerebral lumbar nerve, for comparison, he cries out, raises himself up and struggles. In general it appears that the sensibility of the ganglions is infinitely less evident than that of many other organs. Certainly the skin, the mucous system, the medullary, the nervous of animal life, &c. surpass it in this respect.
Our ignorance as to the diseases that have their seat in the ganglions, the distance of those organs from external excitement, prevent our having any data as to their sympathies. I think it very probable, however, that these sympathies take a real part in hysteria, in certain kinds of epilepsy, the paroxysms of which begin, like those of hysteria, by a painful sensation at the epigastric region, in that multitude of affections called nervous, and which the vulgar confound under the name of vapours. One of the most important objects of research in the neuroses, is to determine those that have their particular seat in the nervous cerebral system and those which affect more particularly the system of the ganglions. Place on one side, palsy, hemiplegia, convulsions of infants, tetanus, catalepsy, apoplexy, the greatest part of epilepsies, all the numerous accidents that arise from engorgements, from compressions of the brain from wounds of the head, nervous affections of the sight, hearing, taste, smell, &c. and all the diseases the source of which is evidently in the head; on the other place hysteria, hypochondriasis, melancholia and all that numerous class of affections in which the abdomen and the thorax, the first especially, seem to be the spot in which the evil is seated; you will see that there is an essential difference and that the symptoms have entirely a different character. I do not say that the last kind of nervous diseases affect exclusively the ganglions; for too much obscurity hangs over these affections to pronounce any thing positive as to their seat, or their nature. Undoubtedly even the secretory, circulating, pulmonary organs, &c. can be then particularly affected in their peculiar texture and independently of the nerves they receive; but certainly it is an interesting subject of research, and there is too great a difference in the phenomena of the two orders of affections, not to present differences in their primitive seat. It is difficult to conceive that the system of the ganglions has not a great part in the last order.
That which induces me to think that the difference of the phenomena that the general order of neuroses presents us, arises particularly from the difference of the cerebral nerves and of those of the ganglions, is that their phenomena in a state of health are very different. Hallé has observed very well that the pains that are experienced in the parts in which the nerves coming from the ganglions are distributed, have a peculiar character, and that they do not resemble those that are felt in the parts where the cerebral nerves are sent. Thus the painful sensation that is experienced at the loins in affections of the womb, by vinous injection made into the tunica vaginalis, &c. a sensation that appears to me to arise from the sympathetic influence exercised by the organ affected upon the lumbar ganglions, the pains of the intestines, the burnings at the epigastric region, &c. &c. do not resemble pains of the external parts; they are deep, and go to the heart, as we often say. We know that there are colics essentially nervous, which are certainly independent of every local affection of the serous, mucous, and muscular systems of the intestines. These colics are evidently seated in the nerves of the semi-lunar ganglions, which are spread along the whole course of the abdominal arteries. They are real neuralgias of the nervous system of organic life; now these neuralgias have absolutely nothing in common with the tic douloureux, sciatica, and other neuralgias of the nervous system of animal life. The symptoms, the progress, the duration, &c. every thing is different in these two kinds of affections.
What I have just said upon the injuries of sensation, applies also to those of motion. No kind of comparison can be made between the convulsions of the muscles that receive the nerves of animal life, and the spasmodic and irregular motions which arise in all the muscles that receive nerves from the ganglions. Nothing resembles tetanus in the heart, the intestines, the bladder, &c.
All these considerations establish striking differences between the cerebral nerves and those of the ganglions; differences upon which I can only present approximations, as we have no data as to the functions of the last.
IV. Development.
The ganglions differ essentially from the brain in the early periods in their development, which is proportionably much less advanced than that of the brain. They are only on a level with all the other organs, whilst this is infinitely superior to them in this respect, as we have seen. By comparing the superior cervical, semilunar ganglions, &c. in the fœtus, and in the adult, it is easy to make this remark. The ganglions receive also less vessels in proportion than the brain. They do not follow the proportion of increase of the organs to which they send nerves. Thus those that furnish the genital organs, which are nearly nothing during the first years of general nutrition, are as large in proportion as those which go to the liver, the stomach, the intestines, which are characterized by an early increase. These nerves follow in this respect the same law as the ganglions, though the most are found upon the arteries, which are more or less developed according to the organs they penetrate.
The nervous system of organic life being less early in its development than that of animal life, should be subject in infancy to fewer affections; and this is what is observed. Convulsions, and most of the neuroses of the second, are, as we have seen, a peculiar appendage upon infancy. On the other hand, the particular order of nervous affections of which we have spoken, and in which it appears that the first takes the principal part, is generally less frequent at this period. All nervous diseases, whose peculiar seat seems to be at the epigastric region, in which there is so great an abundance of nerves coming from the ganglions, appear to be foreign to this age.
Another difference that distinguishes the ganglions from the brain as it respects development, is this, that in the fœtus, they are not, like it, of extreme softness. Their hardness is little inferior to what they afterwards possess in adult age.
In proportion as we advance from infancy, the organic nervous system begins to become predominant. It is towards the thirtieth or fortieth year that it appears at its maximum of action; it diminishes as we approach old age; it decays in part at this epoch. The nerves become greyish; the ganglions are hard, resisting and smaller. The neuroses that appear to belong to them are infinitely more rare. Moreover, the obscurity that rests upon the functions of this system, does not allow me to point out definitely the alterations they experience in the different ages.
V. Remarks upon the vertebral ganglions.
In all that I have said thus far upon the ganglions, I have not noticed those which correspond with the foramina through which the nerves pass, and which some call simple ganglions. We know that at the instant each nerve goes from each of these foramina, it exhibits an evident enlargement, reddish, pulpy, analogous in its appearance to most of the ganglions. I confess, that I know not how to class these organs. We cannot deny that they have the greatest analogy in structure to the others. They are approximated in another respect, which is this, that the nerves, in going from them, form almost immediately plexuses that we have designated under the names of cervical, brachial, lumbar, and sacral, in the same way as the solar, cardiac, mesenteric plexuses, &c. are formed by the nerves of organic life, at the moment they go from their respective ganglions. However, these last nerves are conductors of very different properties. Irritate in a living animal the superior cervical ganglion, the inferior even, which is more difficult, though it may be come at, the muscles to which they send nerves will remain unmoved; the same phenomenon takes place by exciting the nerves themselves. On the contrary, every irritation of a filament coming from the vertebral ganglions, produces immediately convulsions in the corresponding muscles. The sensibility is entirely different in the two species of nerves. Besides, there is no analogy between the manner in which the nerves go in all directions from the vertebral ganglions, and that in which the other ganglions furnish theirs. In the expectation that further experiments may elucidate the subject, let us content ourselves with pointing out what is the result of accurate observation.
ARTICLE SECOND.
OF THE NERVES OF ORGANIC LIFE.
I. Origin.
Each ganglion is, as we have seen, a centre from which go in different directions, various branches, the whole of which form a kind of little separate nervous system. The manner of the origin of these branches has but very little relation with that of the branches of the brain and of the spinal marrow. The following are some differences that distinguish it.
1st. The adhesion is much stronger; the nerve breaks any where else rather than at its origin; the opposite of this takes place in the preceding system. 2d. It does not appear that the substance of the ganglion is continued in the nerve to form the medullary substance of it, since the organization of the one and the other is very different. Sometimes, however, the ganglion is continued for a short distance in the form of a cord. This happens especially in the superior cervical, in the lumbar, the semi-lunar, &c. Then the form only is different; but it is easy at the first view to distinguish where the ganglion ends and the nerve begins. 3d. This beginning is made in a sudden manner; it is like a muscle implanted in a tendon. The best manner of seeing this arrangement to advantage is to cut longitudinally the superior cervical ganglion and the cord it sends to the inferior; the change of nature of the one and the other is then very apparent; or, if we consider the ganglion as a division of the numerous filaments of the nervous cords, we distinguish very well the sudden change that these filaments experience in passing from the cord to the nerve. 4th. The dense cellular covering that surrounds the ganglion is continued upon the nervous origin, and gives it an increase of consistence at that place. This must be carefully raised before we come to the nerve. We see then each distinct filament arising from the ganglion. After it has gone from it, sometimes it remains separate; this takes place at the semi-lunar, the lumbar, the opthalmic, whose elongations are of great delicacy. Sometimes many of these filaments unite together and form a cord as between the two cervical, as at the great and small splanchnic nerves, &c.
I have not been able by maceration, ebullition, or the action of the acids to destroy the adhesion of the nerve with the ganglion, as we destroy that of the muscle with the tendon, of this with the bone, &c.
II. Course, Termination, Plexuses.
The nerves after going from the ganglions, are distributed in many different ways which we shall now examine.
1st. There are always some which go immediately to communicate with the system of animal life. The ophthalmic ganglion sends branches to the motores communes, and to the nasal nerve. The spheno-palatine communicates with the superior maxillary nerve; the superior cervical with all the nerves that surround it, viz. above with the motor externus, within with the great hypoglossal, the par vagum, the glosso-pharyngeal, the spinal, &c.; behind with the first cervical pairs. All the ganglions situated above each other along the vertebral column, send communications through each pair of foramina that correspond with them. The par vagum communicates with the semi-lunar, &c. It is not then any separate ganglion of the nerves of animal life; hence the common expression that designates each ganglion as arising from this or that pair, or being found in its course, is very inaccurate. Thus the opthalmic is by no means in the course of the common motor nerve. The one and the other send each a branch, which unites; or rather there is a branch of communication between the ganglion and the cerebral nerve. In general all these branches of communication with the system of animal life, are short, whitish, and of the same nature, or at least of the same appearance as the nerves of this last. They do not form any plexus in their course, rarely furnish branches, and appear to have no other use than that of establishing anastomoses between the two systems.
2d. Each ganglion sends above and below branches to the two ganglions that are contiguous to it. We have seen that the opthalmic and the spheno-palatine are exceptions to this rule. Sometimes also, as I have said, there are interruptions in other regions. Notwithstanding this, these general communications make us regard the ganglions as being connected every where, and able to receive from each other the different affections of which they can be primitively the separate seat. These branches of communication are straight as in the preceding, sometimes very fine, as between the lumbar and sacral ganglions, at other times larger, as that which is between the two cervical, superior and inferior, in some cases very large, as the great splanchnic, which is a real trunk of communication between the intercostals and the semi-lunar. The nerves that we are now considering, the last especially, have like the preceding, an arrangement exactly analogous to the cerebral nerves; they are formed of whitish cords, which are the result of filaments. The eye discovers no difference between them.
3d. Many filaments coming from ganglions, go to certain cerebral muscles, as to the diaphragm, some of those of the neck, &c.; others go to neighbouring organs only.
4th. The greatest number going from the ganglions in separate filaments, interlace in the form of a plexus with those of the contiguous ganglions, in the neighbourhood of, or upon the great vessels. The most remarkable plexus is the solar, composed by the innumerable branches that come from the semi-lunar; then we see the hypogastric, the cardiac, &c. The greater number of these plexuses are not exclusively formed by the nerves of organic life; those of the animal give some to them also, as the par vagum furnishes an example for the solar and the cardiac, as the sacral nerves afford another for the hypogastric, &c. However the nerves of organic life always predominate in these plexuses. There is only the pulmonary in which the par vagum particularly predominates, whilst the nerves coming from the inferior cervical ganglion are, if we may so say, but accessory.
The primitive plexuses resulting from the interlacing of the organic nerves at their exit from the ganglions, form a mass of irregular nerves, buried in the cellular texture, accommodated to the forms of the neighbouring organs, and wholly different from those of animal life, as of the brachial, the lumbar, &c.
In fact, the filaments at every instant, not only place themselves as in the preceding ones, at the side of each other, at every change of position; but their extremities continue; they interlace with each other, change at every point the direction, form networks, and mix so together, that it is not possible to distinguish any thing except a thousand nerves, that we might say grew up under the cloth with which we wiped the place where the plexus was found.
These organs are remarkable for their reddish or greyish colour, for their softness, for their indistinctness, &c.; it is often difficult to distinguish them from cellular texture. The best manner of making them evident is to let the subject macerate for a day or two open in the water; they whiten then sensibly, do not soften, and appear even to increase in consistence, like the cerebral nerves in a similar case. Besides their delicacy is such, that it is impossible to submit them to any kind of reagents. Only I have observed that they possess in an eminent degree the property of horny hardening, and that they do not yield in this respect to the cerebral. This delicacy depends upon this, that all the filaments are separate from each other, instead of being like the preceding, collected into cords; it is this also that makes these nerves so numerous. If all the filaments of the brachial plexus were separated like those of the solar, they would present the same appearance and the same number in their interlacing.
Do the primitive plexuses formed by the ganglions perform a part in the nervous functions? are they centres to which are referred important phenomena? What has not been said upon this subject, concerning the solar plexus? But nothing, I believe, of all that has been advanced is founded upon accurate observation.
The plexuses of organic life are soon separated into different divisions, which go to different parts, to those especially of this life. These divisions arise from an infinite number of little filaments which go constantly separate, though placed near each other, and which never unite into cords like the preceding. They accompany almost all the arteries; thus the renal, the hepatic, the splenic, the coronary stomachic, the mesenterics, the hypogastric, the carotid and its distributions, &c. are surrounded with filaments coming from ganglions. These filaments go in two ways. 1st. Some accompany the artery without being connected with it; considerable cellular texture separates them; they go in its course without intermixing in a sensible manner with it. 2d. The others form for it, if we may so say, a new coat, exterior to the others, which adhere to it intimately, and which interlace so together, that they might be taken for a network surrounding the artery.
When the artery runs but a short course, these two orders of branches remain distinct from each other as far as the organ, as we see around the splenic, the hepatic, the renal, &c.; but if the course is longer, the external branches gradually get into the plexus, and are entirely lost there. This plexus can be followed upon the great trunks; it divides upon each branch, and can be still seen; but such is its tenuity upon the minute ramifications that it disappears there entirely. The spermatic is one of the arteries upon which it can be traced the longest. The arteries of the extremities appear to be destitute of it. In general it is upon those that go to the central organs of internal life, that this network is the most evident. When we deduct from the sum of the filaments coming from the ganglions, those by which they communicate on one part with each other, and on the other with the nerves of animal life, we see that almost all the rest is finally destined to accompany the arteries. This arrangement is wholly different from that of the cerebral nerves, whose filaments are only in apposition with the vessels. These make almost an integrant part of them, the adhesion is so intimate; this certainly supposes a use of which we are ignorant, relative to the circulation, or to the other organic functions. As these vessels distribute every where the materials of these functions, of the secretions, exhalations, nutrition, &c. the organic nerves have no doubt some influence upon them. Neither experiment or observation have taught us any thing upon this point.
The veins are not accompanied by so many organic nerves. It is the same as it respects the absorbent trunks, which go almost every where separate from this system.
The constant union of the arteries with the organic plexuses, an union that presents an arrangement wholly different from that of the ganglions, has undoubtedly an influence upon the action of these plexuses, or rather upon that of the nerves that go from them, by the motion the blood communicates to them. It should be remarked upon this subject, that as nature has placed a crowd of arteries at the base of the brain to agitate it with an alternate motion, she has put also the most considerable plexus of the whole organic system upon one of the places to which the red blood communicates the strongest impulse, viz. upon the trunk of the cœliac.
III. Structure, Properties, &c.
From what has been said above, it is evident that the nerves going from the ganglions are of two sorts as it respects organization; 1st. those that are identified with the cerebral system, by their white colour, by the possibility of dividing their trunks into distinct cords, and these into filaments, which appear to have nervous coats and medullary substance like the preceding; 2d. those which present only little separate filaments, greyish or reddish, soft, and which are seen in prodigious numbers in the plexuses. Have these a nervous coat and a medullary substance? It is impossible to determine it.
The properties of texture are ascertained with difficulty in the organic nerves. As to vital properties, it is undoubted that the animal sensibility is not as much raised in these nerves as in those of animal life. I have often laid bare the plexuses in the abdomen; then by letting the animal rest a moment, and by irritating them comparatively with the lumbar nerves, I have uniformly made this remark. We know that very frequently the ligature of the spermatic artery is not painful in sarcocele, though the branches coming from the ganglions form for it a plexus like a network, which can in no way be separated from it. If we draw out a portion of intestines by a small wound in the abdomen, the irritation of the sub-mucous layer at the side of the vessels, is hardly felt, though many nerves of ganglions are found at this place. I have had numerous occasions to act in different ways upon the carotid, to which the superior cervical ganglion furnishes branches from above; now, as long as I did not touch the par vagum, the animal remained tranquil. I am far, however, from believing in the absolute insensibility of the nerves of the ganglions; but certainly under the circumstances that I have related, the cerebral nerves would have caused much more pain to the animal.
I think that in a morbid state this sensibility is susceptible of being greatly raised. We certainly cannot deny but that the solar plexus takes a great part in the different sensations that are experienced at the epigastric region; the very acute pains that often attend the formation of aneurisms, are probably owing in part to the distension of the nervous filaments that surround the artery. I have already said that it is probable that the organic nerves are much concerned in the different sensations that are produced by some peculiar neuroses.
These nerves occasion evident sympathies in certain cases. It is to this that must be referred the different affections that Petit de Namur has produced in the organ of sight, by irritating their branches that are accessible. The development of the nerves of the ganglions follows nearly the same laws as that of those organs from which they emanate.
Let us observe in finishing this system, that there is no one that ought to arrest the attention of physiologists more. All the others present a series of phenomena already well known. Of this, we have hardly any knowledge. It does not present as yet, if we may so say, but some of the negative attributes of the nervous system of animal life. Thus it is without doubt that the organic nerves do not have the same part as the preceding in animal sensibility; that they are always foreign to contractility of the same species; that they have no direct influence upon the sensible organic, since as we shall see, we can cut or irritate them without destroying or hastening the motion of the muscles to which they go. But in knowing the parts they do not perform we are ignorant of those to which they are really destined. I have already observed that the difficulty of making experiments upon the ganglions and the plexuses, will much retard the progress of science. We have scarcely any branches upon the exterior upon which we can act.
Scarpa has collected the opinions of all who have preceded him, together with his own, upon the uses of the ganglions. I refer to what he has said upon this subject. As the general point of view in which he has presented these organs, and that in which I offer them here, differ essentially, the account that I have just given of the nerves of organic life has necessarily a general stamp wholly different from that of his work, a work, however, which, like all this author has published, confers the greatest honour upon the state of anatomy at the period in which we live.
I will terminate this article by an important reflection. If the nerves were only divided to form the ganglions, if these presented in their interior only differences of forms, and a very minute division of their filaments, why should they be so constant in animals? Many organs are wanting, vary, are presented under a thousand various forms in their different classes; on the contrary, the ganglions are constant. In those species even in which the cerebral system is imperfect, that of the ganglions is complete in its organization. Animal life diminishes and is contracted in an evident manner in most insects, in worms, &c. and generally in animals without verterbræ. The brain and the nerves become less evidently marked in proportion as this life is less perfect. The organic is, on the contrary, almost in its perfection in these animals. The ganglions and their nerves are also very evident. This remark has struck me in reading the researches of different authors upon the anatomy of the lower classes of animals; now, if the ganglions were not the centres of certain important functions of which we are ignorant, would they be so invariable in the animal organization?